1. Field of the Invention
The present invention relates to a bag mouth opening device in which both side surfaces of the mouth of each one of continuously conveyed bags are suction-chucked by a pair of suction-chucking members disposed on both sides of the conveying path of the bags, and then the suction-chucking members are moved away from each other so as to open the mouth of the bag.
2. Prior Art
Follow-reciprocating type devices, rotating loop type devices, suction-chucking belt type devices, etc. have been known as conventional bag mouth opening devices used in continuous conveying type bag-filling packaging machines.
In the following-reciprocating type devices, suction-chucking members repeat a reciprocating movement that includes a following movement in the bag conveying direction stoppingxe2x80x94return movementxe2x80x94stopping, and the mouth of a bang is opened during the following movement. Such a device is described in, for instance, Japanese Utility Model Application Publication (Kokoku) No. H3-12645.
However, the following-reciprocating type devices have drawbacks. First, a distance sufficient to accelerate the suction-chucking members from a stopped state to the conveying speed of the bags and a distance sufficient to decelerate and stop the suction-chucking members following the opening of the bag mouths are required. Thus, the distance for the reciprocating movement of the suction-chucking members tends to be long by a corresponding amount, resulting in an increase in the size of the packaging machine as whole, and a large installation space is also required. Second, time is required for acceleration and deceleration, thus hindering any increase in the operation speed of the packaging machine. Third, since a reciprocating movement is repeated, considerable vibration and noise are generated, causing deterioration in the quality of the work environment. This problem becomes conspicuous as the packaging machine is operated at higher speeds. Fourth, in cases where a plurality of sets of suction-chucking members are installed so that a plurality of bags are subjected to mouth opening at one time, the inertia increases, so that an even greater time and distance are required for acceleration and deceleration. As a result, the size of the apparatus tends to become larger, making it very difficult to increase the speed as desired.
In the rotating loop type devices, suction-chucking members are disposed at equal intervals on a chain mounted on a plurality of sprockets, and these suction-chucking members are caused to revolve at the same speed as the conveying speed of the bags. A part of the revolving path of the suction-chucking members is set so as to run along the conveying path of the bags, and the mouths of the bags are opened in this area. For example, such devices are described in Japanese Patent Application Laid-Open (Kokai) Nos. S59-221201 and S60-110624. A similar device is also described in Japanese Patent Application Publication (Kokoku) No. S44-18473.
The problems of these devices are that the structure is complex, and the maintenance and cleaning characteristics are poor. In addition, the cost of the device is high; and since the device is large in size, a large installation space is required for the packaging machine as a whole.
Furthermore, in the suction-chucking belt type devices, a pair of endless belts that have suction holes are caused to rotate at the same speed as the conveying speed of the bags. The belts are disposed so as to contact both surfaces of the bags symmetrically from either side of the bag conveying path and then separated from each other while moving. Such devices are described in, for instance, Japanese Patent Application Publication (Kokoku) No. S61-49170 and Japanese Patent Application Laid-Open (Kokai) No. H6-80122.
However, the suction-chucking belt type devices have problems in addition to those seen with the rotating loop type device. The suction-chucking belt type devices perform the mouth opening operation (suction and then separation) from one end of each bag. Accordingly, though this system is suitable for gazette bags (bags with both sides near the mouth folded into inside), mouth opening errors tend to occur in the case of ordinary flat bags or self-standing bags.
Accordingly, the present invention is to solve the problems encountered in such conventional bag mouth opening devices used in continuous conveying type bag-filling packaging machines.
Thus, it is an object of the present invention to provide a bag mouth opening device that is simple in structure and is more compact and that makes it possible to increase the operation speed of the device with little generation of vibration or noise.
The above object is accomplished by a unique structure for a bag mouth opening device for continuously conveyed bags in which both sides of a mouth of each one of the bags that are continuously conveyed at a uniform speed and equal intervals are suction-chucked by a pair of facing suction-chucking members, and then the suction-chucking members are moved away from each other so as to open the mouth of the bag; and in the present invention:
the pair of suction-chucking members continuously revolve:
in mutually opposite directions on circular tracks on a plane that is substantially parallel to a conveying direction of the bags and substantially perpendicular to the surfaces of the bags, and
in a state in which suction-chucking surfaces of the suction-chucking members are kept facing each other; and
time required for the respective suction-chucking members to complete one revolution is set to be at an integral multiple of time required for the each one of the bags to be conveyed over a distance between bags.
Preferably, the pair of suction-chucking members revolve at a constant speed while maintaining positions that are substantially symmetrical with respect to each other and also revolve at the same speed as the conveying speed of the bags.
The pair of suction-chucking members are provided so that each suction-chucking member of such pair is provided on each one of rotation transmitting members, and the suction-chucking member and the rotation transmitting member on which the suction-chucking member is provided perform a translational motion of the same radius of revolution and in the same direction of revolution as each other. The rotation transmitting members that perform the translational motion are always oriented to face in the same direction. Accordingly, the suction-chucking surfaces of the suction-chucking members likewise always face in the same direction (toward the front or face each other) when they are revolving. Of course, the revolution of the pair of suction-chucking members is thus also a translational motion. The mechanism that causes the rotation transmitting members to perform the translational motion comprises, for instance, two rotating shafts that rotate in synchronization in the same direction and respective supporting shafts that are provided in eccentric positions which are offset in the same direction and equal distances and revolve about the rotating shafts as the rotating shafts are rotated. The rotation transmitting members are provided on these supporting shafts and perform the translational motion.
A plurality of sets comprising pairs of suction-chucking members can be disposed along the conveying direction of the bags at intervals that are the same as the distance between bags (between the centers of bags next to each other in the conveying direction). In cases where only a single pair of suction-chucking members are disposed along the conveying path, the time required for the suction-chucking members to complete one revolution is set equal to the time required for each bag to be conveyed over the distance between bags. In cases, on the other hand, where a plurality of sets are disposed, the time required for the respective suction-chucking members to complete one revolution is set at the time obtained by multiplying the time required for each bag to be conveyed over the distance that corresponds to two bags next to each other by the number of sets of suction-chucking members. In this case, it is preferable to set the radius of revolution of the suction-chucking members to increase by the same factor.
The bag mouth opening device of the present invention is used mainly in a system in which bags are conveyed horizontally in the direction of width of the bags with the bags in a vertical attitude and with the bag mouths facing upward by way of suspending the bags with both edges thereof gripped by grippers or by way of holding the bags with retainers, etc. More specifically, the bag mouth opening device is applicable in general to systems in which bags are conveyed in their width direction or in their longitudinal direction with respect to the side surfaces of the bags. Thus, the bag mouth opening device of the present invention can be used in cases in which bags are conveyed in the longitudinal direction or cases in which bags are conveyed in the direction of width or longitudinal direction in a horizontal attitude.
Furthermore, the bag mouth opening device is used not only in cases where bags are conveyed along a straight line but also in cases where, for instance, bags are gripped by numerous grippers disposed around the circumference of a rotating table and are conveyed along a circular track that has a relatively large diameter. In such latter cases, the circular track of the suction-chucking members may be set by way of viewing the tangential direction of the conveying path at the point where the circular track reaches the conveying path (i.e., the suction-chucking point) as the conveying direction.
Furthermore, when bags are conveyed in the direction of bag width with the bags suspended in a vertical attitude, a bag bottom guide is provided in the vicinity of bottoms of the bags so that each one of the constituting elements of the bag bottom guide is disposed on either side of conveying path of the bags, so that the bag bottom guide comes into contact with curved surfaces of the bag and correct such curved surfaces